Two rare cases of benign struma ovarii with malignant recurrence.

Malignant transformation of struma ovarii is very rare (<5%). Diagnosis of HDFCO without extra ovarian dissemination is difficult due to the resemblance of its histological appearance with normal thyroid tissue. There is no consensus on the postoperative treatment of malignant struma ovarii (MSO). Clinical and histological features of MSO should be assessed for the postoperative treatment decisions. TSH suppression and thyroglobulin level measurements are necessary for patient follow-up.